Step 2 – Flip duplicate

Step 3 – Reduce Opacity and position

Lower the layer’s Opacity down to 20% to reveal the image below. Place and rotate the reflection into place. Use Free Transform to rotate the reflection if you need to, to line it up with the existing horizon.

Step 4 – Add and edit layer mask

Once the reflection is in place, add a layer mask. Now you can use the Brush tool set to black to paint away the parts of the image above the horizon.

Step 5 – Blend mode

Increase the Opacity of the layer up to 70% and then set its blend mode to Soft Light. This will help merge the two together.

Step 6 – Apply Wave filter

Add the Wave filter from the Distort options in the Filter menu. Keep slider values low, setting Scale to around 10. This will depend on the resolution of the image, however. Hit OK and this should complete the effect.